Similarities and differences between the solar wind light noble gas compositions determined on Apollo 15 SWC foils and on NASA Genesis targets

We compare the solar wind (SW) He, Ne, and Ar compositions collected during the Apollo Solar Wind Composition (SWC) experiments (1969-1972; Al-& Pt-foils) and the Genesis mission (2002-2004; so-called DOS targets considered here). While published SW Ne-20/Ne-22 and Ar-36/Ar-38 ratios of both data sets agree, differences exist in the He-4/He-3, He-4/Ne-20, and Ne-20/Ar-36 ratios. However, Ne-20/Ar-36 ratios from Apollo-16 Pt-foils, exclusively adopted as SW values by the SWC team, are consistent with the Genesis results. We investigate if the differences indicate a variability of the SW over the course of about 30 yr, or systematic biases of the two data sets, which were collected in different environments and measured several decades apart in different laboratories (University of Bern; ETH Zurich). New measurements of Apollo-15 SWC aluminum foils in Zurich generally agree with the original measurements performed in Bern. Zurich samples show slightly lower He-4 concentrations suggesting a few percent of diffusive loss of He-4 during storage of the foils. A 3% difference between the He isotopic ratios measured in Bern and in Zurich possibly represents an analytical bias between the laboratories. The low SW He-4/Ne-20 and Ne-20/Ar-36 ratios in Apollo-15 Al-foils compared to Genesis data are consistent with a mixture of Genesis-like SW and noble gases from small amounts of lunar dust. Our data suggest that the mean SW He, Ne, and Ar isotopic and elemental compositions have not significantly changed between the overall Apollo and Genesis mission collection periods.